This invention relates to a hybrid electric vehicle and more particularly, to a hybrid electric vehicle having a limited operation strategy which provides a driver or user with limited operation of the vehicle in the presence of faults within any of the power train subsystems.
Hybrid electric vehicles (xe2x80x9cHEVxe2x80x9d) utilize both an internal combustion engine and one or more electric motors to generate power and torque. One type of hybrid electric vehicle, commonly referred to as a xe2x80x9cparallelxe2x80x9d or xe2x80x9cpower splitxe2x80x9d type hybrid electric vehicle, includes three power train subsystems which cooperatively provide the torque necessary to power the vehicle. Particularly, a xe2x80x9cpower splitxe2x80x9d type hybrid electric vehicle includes an engine subsystem (e.g., an internal combustion engine and controller), a generator subsystem (e.g., a motor/generator and controller), and a motor subsystem or an xe2x80x9celectric drive subsystemxe2x80x9d (e.g., an electric motor and controller).
In this type of HEV power train configuration, there are two xe2x80x9cpower sourcesxe2x80x9d that are connected to the drive line: 1) a combination of engine and generator subsystems which are interconnected by use of a planetary gear set, and 2) the motor subsystem. In the first power source, the engine connects to the carrier of the planetary gear set, the generator connects to the sun gear of the planetary gear set, and the ring gear of the planetary gear set outputs power from the engine and/or from the generator to the drive line. By controlling the generator appropriately, the planetary gear set serves as a power split device that splits the engine output to the generator and to the drive line as desired, and as a continuous variable transmission (xe2x80x9cCVTxe2x80x9d) between the engine and the ring gear which is connected to the drive line. The second power source, (e.g., electric motor) drives the ring gear and provides propulsion to the vehicle independently from the first power source. In this manner, the two power sources can provide propulsion to the vehicle simultaneously and independently.
This hybrid configuration provides improved fuel economy, and reduced emissions since the internal combustion engine can be operated at its most efficient/preferred operating points by use of the previously described xe2x80x9cCVTxe2x80x9d function. Additionally, this configuration can achieve better driveability, and may extend vehicle performance relative to a comparative conventional vehicle. In order to achieve the goal, appropriate coordination and control between subsystems in the HEV are essential. This goal is achieved by use of a central vehicle system controller (xe2x80x9cVSCxe2x80x9d) and a hierarchical control architecture.
Hybrid electric vehicles typically use a VSC to interpret driver inputs (e.g., gear selection, accelerator position and braking effort), to coordinate each of the vehicle subsystems, and to determine the vehicle system operation state. The VSC generates commands to appropriate subsystems based on driver inputs and control strategies, and sends the generated commands to the respective subsystems effective to cause the subsystems to take appropriate actions to meet the driver""s demands.
While the foregoing control strategy is effective to efficiently operate the vehicle under normal operating conditions, it suffers from some drawbacks. Particularly, if a fault occurs in any one or more of the vehicle""s power train subsystems, the vehicle may no longer be driveable, thereby leaving a driver or operator stranded.
There is therefore a need for a hybrid electric vehicle which includes a limited operation strategy which allows the vehicle to continue to function and drive in the presence of a fault in one or more of the power train subsystems.
It is a first object of the invention to provide a hybrid electric vehicle which overcomes at least some of the previously delineated drawbacks of prior hybrid electric vehicles.
It is a second object of the invention to provide a hybrid electric vehicle which includes a limited operating strategy which allows the vehicle to be driven when a fault occurs in one or more of the vehicle""s power train subsystems.
It is a third object of the invention to provide a hybrid electric vehicle having a power split configuration and allowing certain portions of the power train to operate when other portions are inoperable.
It is a fourth object of the invention to provide a limited operation strategy for fault management which controls and coordinates the functioning power train subsystems in the hybrid electric vehicle when one or more of the power train subsystems is in a fault condition, thereby providing the driver with xe2x80x9climp home operationxe2x80x9d if possible.
According to a first aspect of the present invention, a hybrid electric vehicle is provided. The hybrid electric vehicle includes a drive train; an engine subsystem which is operatively coupled to the drive train and which selectively provides torque to the drive train; a generator subsystem which is operatively coupled to the drive train and which selectively provides torque to the drive train; an electric motor subsystem which is operatively coupled to the drive train and which selectively provides torque to the drive train; and a controller which is communicatively coupled to the engine subsystem, to the generator subsystem, and to the electric motor subsystem. The controller is effective to detect whether a fault exists in any of the subsystems, and upon the detection, to allow the hybrid electric vehicle to operate by use of less than all of the subsystems.
Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.